In extracorporeal blood treatment, blood is taken out of a subject, treated and then reintroduced into the subject by means of an extracorporeal blood flow circuit. Generally, the blood is circulated through the circuit by one or more pumping devices. The circuit is connected to a blood vessel access of the patient, typically via one or more access devices, such as needles, which are inserted into the blood vessel access. Such extracorporeal blood treatments include hemodialysis, hemodiafiltration, hemofiltration, plasmapheresis, bloodbanking, blood fraction separation (e.g. cells) of donor blood, etc.
In extracorporeal blood treatment, it is vital to minimize the risk for malfunctions in the extracorporeal blood flow circuit, since these may lead to inefficient treatment due to impaired delivery of hemodialysis prescription having potentially severe effects on the condition of the subject.
Malfunctions may be caused by i) accidental misplacement of the access devices for blood extraction (withdrawal and return, e.g. arterial and venous needles/catheters) or ii) faulty connection of the access devices to the blood lines. For instance, the connection of the access devices to the blood vessels may be reversed, causing recirculation of the treated blood during extra-corporeal circulation such that the dialyzed blood returning through the venous line is drawn back into the arterial line without having passed through the heart and thereby reducing the treatment dose given to the patient, which may have negative consequences to the patient's health both in the short and long term perspective. Another example of malfunction includes a reversed connection of the blood lines to the access devices.
These malfunctions all originate in a “connection system” between the patient and the extracorporeal blood flow circuit. The connection system includes one or more access devices and possibly one or more releasable connectors for attaching the access devices to tubing in the extracorporeal blood flow circuit.
Recirculation in extracorporeal blood treatment arises when the whole or a fraction of treated extracorporeal blood flow returns directly to the inlet of the extracorporeal blood line instead of flowing back to the heart.
There are several reasons for recirculation, for instance a) low access blood flow Qa compared to the blood flow Qb of extra-corporeal circulation, specific problems related to the b) blood access physiology or return of treated blood directly to inlet due c) to too close positioning of needles. However, another common cause for needle problems is accidental misplacement of the arterial and venous access devices or tubes to reversing the configuration and causing a substantial recirculation and significant reduction of treatment dose.
To avoid recirculation of the treated blood during extra-corporeal treatment the arterial access must be placed in an upstream position compared to the venous access. Studies have shown that reversed needles fault may occur in approximately one of ten treatments.
Situations with access recirculation require intervention. To this end, an apparatus for extracorporeal blood treatment may include one or more surveillance devices that detect either recirculation in general or specifically the reversal of the needles.
Methods of access surveillance include clinical examination, urea or tracer recirculation measurement, continuous wave Doppler methods, duplex ultrasonography, and radiograph angiography.
A method involving continuous wave Doppler measurements to detect access function related recirculation by ultrasound dilution is disclosed in EDTNA ERCA J 1998 April-June; 24(2):3-6 “Theoretical and practical issues in recirculation; assessment of vascular access”. This method involves continuous wave Doppler measurements where a reversed position of the needles is detected by the Doppler frequencies being higher with the pump on than with the pump off.
Urea recirculation measurements involves comparing the blood urea taken from the access lines with that from a peripheral vein. When there is no recirculation, the urea in the arterial line and peripheral vein should be the same. However, this method will measure not only any access recirculation, but also the so called cardio-pulmonary recirculation. Cardio-pulmonary recirculation occurs because the treated blood traveling back towards the heart will mix with blood returning from the body, be pumped by the heart through the lungs and back to the heart where it will be pumped back into the body, and a fraction of this arterial blood is directed towards the access. This means that a fraction of the blood going out to the access will come from the newly treated blood. Just as with access recirculation this cardio-pulmonary recirculation therefore causes some newly treated blood to enter the extracorporeal circulation directly, without having passed the main parts of the body in between. This urea method will therefore measure the sum of access and cardio-pulmonary recirculation.
Hematocrit dilution has also been promoted as an indicator. However, the known methods require special training and/or additional laboratory tests. Hence, there is a need for a method for detecting the configuration of withdrawal and return lines in a cardiovascular access that may be applied each time a subject undergoes extracorporeal blood treatment.
No integrated means in dialysis machines exist today which allow automatic detection of reversed needles. Since recirculation does not disturb the treatment in any other way than decreasing the treatment efficiency, it may go undetected throughout the whole treatment, and there is a large need for an automatic detection device. Various devices and methods have been disclosed for recirculation measurement, however, none of these are fully integrated and automatic. Furthermore, even if recirculation is detected, there is still a need to distinguish between various causes for recirculation, in particular reversed needles.
One example of another kind of malfunction in the extracorporeal blood flow circuit, which however is not attempted to be remedied by the present invention, is disclosed in JP2006198141. This documents deals with a connection mistake between arterial and venous detection lines between a dialyzer and pressure sensors, resulting in reversed pressure measurements, a potentially directly harmful situation if not discovered in time. Hence, this document relates to a problem and solution which is remote and significantly different from the problem of the present invention.